This invention relates to the production of printed circuitry, and more particularly to a process for accurately aligning a series of printed circuit electrical leads to a series of electrodes on a charge plate for use in ink jet printing.
Coating heads of the type described in Beam et al, U.S. Pat. No. 3,586,907, are used in ink jet printing systems which create printed matter by selective charging, deflecting, and catching of drops produced by one or more row of continuously flowing ink jets. The jets themselves are produced by forcing ink under pressure through a series of orifices in an orifice plate, which is one component of the laminated coating head.
A stimulation arrangement stimulates the jets to break the ink up into uniformly sized and regularly spaced drops, with drop formation occurring in all jets at more or less fixed positions, all located approximately the same distance from the orifice plate. The charge plate is positioned within the coating head so that electrical charging of selected ones of the drops being generated is achieved.
A charge plate of the type used by the Beam et al patent utilizes a plate of dielectric material provided with a series of charging tunnels located equidistantly along a straight line. Each charging tunnel is coated with an electrically conductive material which defines a cylindrical charging electrode. Electrical leads must be connected to each such charge electrode, and the electrical leads in turn are selectively activated by an appropriate data processing system. Typical prior art charge plates including such electrodes are disclosed in Solyst, U.S. Pat. No. 3,975,741, in Kuhn, U.S. Pat. No. 3,984,843, and in Bassous et al, U.S. Pat. No. 4,047,184.
In addition to the difficulties arising in the fabrication of such charge plates, which is described in detail in the commonly assigned copending application of James L. Gudorf, Ser. No. 912,495, filed June 5, 1978 and entitled "Charge Plate and Method of Manufacture", now U.S. Pat. No. 4,195,304 difficulties have also arisen in accurately locating and aligning electrical lead lines with the individual charge tunnels. The difficulty of such an operation will be appreciated when it is remembered that the center-to-center spacing of each charge electrode is only about 0.423 mm and each charge electrode has an internal diameter of only about 0.355 mm, leaving a spacing between charge electrodes of only about 0.068 mm. Moreover, the width of an electrical lead is about 0.18 to 0.20 mm, leaving only about a 0.07 mm tolerance for misalignment with a charge electrode. Depending upon the size of the charge plate and the area to be printed, anywhere from several hundred to over one thousand connections per charge plate must be made.
Previous fabrication techniques involved the use of a multi-step photomechanical reproduction process. These techniques involved the use of one or more masks each containing a repetitive array of elements representative of the electrical leads to be formed ultimately on the charge plate. By a succession of alignment and fabrication steps such as deposition and/or etching, the finished device would be produced.
However, these techniques required both the accurate production of photomasks and the repeated accurate registration and alignment of them on the charge plate substrate. The problem of avoiding accumulation of error in such techniques is both difficult and expensive. Moreover, if the charge tunnel spacing and diameter on the charge plate is not exact, further alignment errors are introduced into the device. Since fabrication techniques are not perfect, slight size and spacing errors are almost unavoidable in forming charge tunnels. Thus, an accumulated alignment error of only a few thousandths of an inch (or hundredths of a millimeter) may result in either a missed connection or a short circuit.
Accordingly, the need exists in the art for a more reliable and accurate process for generating and aligning charge plate artwork (i.e. electrical leads and the like).